One of the most common techniques used to increase oil recovery is gas injection. The gas injection can be either miscible or immiscible depending on the injection pressure. Miscibility can be reached when the pressure exceeds the minimum miscibility pressure (MMP). Temperature and pressure are important factors that usually affect the MMP. Oil properties play an important role in the success of miscible injection, with the miscible gas injection working optimally when oil is light. Here, we performed data analysis based on more than 1500 experiments, simulation and field tests from more than 170 researchers to show the conditions at which miscible injection can be applied. We investigated various gases, including carbon dioxide (CO2), nitrogen (N2), and hydrocarbon gases. Different statistical analysis tools, including histograms, boxplots, and cross-plots, are used in this study. The data demonstrate that CO2 is the most commonly used gas during miscible injection. The majority of studies performed their experiments at temperatures between 40 to 100 °C using oil with a viscosity of 0.25 to 1.5 cp, and an API gravity between 35.1 to 45 °API. Since a variety of gases have been investigated in this research, a variety of MMP has been reported.
Gas Enhanced Oil Recovery (GEOR) has been used widely for decades to increase the oil recovery from hydrocarbon reservoirs. Researchers have experimented with the use of different types of gases to be injected into the reservoirs, with the aim of increasing oil production. These gases include Carbon Dioxide (CO2), Nitrogen (N2), Methane (CH4), Ethane (C2H8), and Propane (C3H12). These gases have been thoroughly researched over the past decades, and many have been proven to be successful in enhancing oil recovery (Crawford, et al., 1978; Lee, and Reitzel, 1982; Hudgins, et al., 1990; Kulkarni, and Rao, 2005; Adel, et al., 2018). Gas EOR is injected into the reservoir by different methods; continuous gas injection, which involves injecting the gas continuously without any other fluid, water alternating gas, where gas and water are injected in consecutive cycles, and cyclic gas injection, which also known as ‘huff-n-puff’. The consecutive cycles method, the same well is used for injection and production by injecting the gas multiple times for soaking and production. This method has proven its success in conventional reservoirs (Issever, et al., 1993; Miller, et al., 1994; Lino, 1994; Kanfar and Clarkson, 2017).